The present invention relates to a grinding apparatus provided with a grindstone for working, for example, spline ball grooves on the inner surface of a workpiece and a dressing method for dressing the grindstone.
There are known grinding apparatuses that use a grindstone to form spline ball grooves on the inner surface of a workpiece. One such conventional grinding apparatus comprises a spindle mechanism, which is rotated by means of a motor, and a substantially disc-shaped grindstone rotatable by means of the spindle mechanism. As the grindstone rotates and moves in the axial direction of the workpiece, its outer peripheral portion grinds the inner surface of the workpiece. The grindstone is rotatably supported by means of a bearing of the spindle mechanism. A pulley is coupled to the grindstone. Another pulley is coupled to the rotating shaft of the motor that is situated at a distance from the grindstone. An endless belt for power transmission is passed around and between the two pulleys.
The rotation of the motor is transmitted to the grindstone by means of the pulleys and the belt. The axis of the spindle mechanism extends parallel to that of the workpiece. The spline ball grooves are ground as the grindstone rotates and moves parallel to the axis of the workpiece so that its outer peripheral portion touches the inner surface of the workpiece. This conventional grinding apparatus cannot use a bearing that has a diameter larger than that of the disc-shaped grindstone. Accordingly, the bearing cannot enjoy good stiffness to resist grinding force.
Thus, according to the conventional grinding apparatus described above, it is hard to augment grinding forces in the tangential and normal directions of the circular grindstone that are needed to grind the workpiece. In some cases, therefore, the grinding efficiency is low, and the surface accuracy of the spline ball grooves is not high enough. Since the bearing has a small diameter, moreover, it is subjected to too heavy a load of grinding to enjoy a long life. Since the belt is small-sized, furthermore, its tension or durability may be unsatisfactory.
As shown in FIG. 13, some conventional grinding apparatuses may use a single-point dresser 101 for dressing a grindstone 100. According to a dressing method using this dresser 101, however, it is ground at an angle xcex8xe2x80x2 to a center 100c of the grindstone 100 (so-called interference grinding), so that a distal end face 102 of the grindstone 100 cannot easily have a given curvature radius and is subject to undulation. Further, it is hard for the dresser 101 accurately to dress and shape a grindstone for grinding a groove in the form of a Gothic arch.
FIG. 14 shows shape errors of a Gothic-arched groove ground with use of the grindstone 100 that is dressed by means of the conventional dresser 101. A target value of a curvature radius R of the groove for a contact angle xcex8 of 45xc2x0 is 3 mm. In this case, the target value can be substantially secured for positions near 45xc2x0 (xcex8=40xc2x0 to 50xc2x0). At its bottom or shoulder portions, however, the groove is subject to considerable shape errors, as indicated by a segment 103.
In the case where a formed dresser is used for dressing, on the other hand, the grindstone may possibly fail to come into entire contact with the dresser, owing to thermal deformation of the spindle mechanism for the grindstone or a dresser rotating mechanism. Conventionally, this problem is solved by a known technique that is described in Jpn. Pat. Appln. KOKAI Publication No. 3-19770, for example. This technique is a method in which the axial displacement of a grindstone is detected by means of a noncontact sensor, and dressing is carried out after dislocation corresponding to the displacement is corrected. Although this conventional technique can be effectively applied to a small-diameter grindstone for inner surface grinding, it cannot be used to dress a large-diameter grindstone for outer surface grinding or a pencil-type grindstone.
In Jpn. UM Appln. KOKAI Publication No. 61-169564, there is described an apparatus for transmitting ultrasonic vibration, which is generated as a rotary dresser and a grindstone come into contact with each other, to an acoustic emission sensor through the medium of a liquid, in order to detect contact between the dresser and the grindstone. In this conventional apparatus, however, the liquid for use as the ultrasonic propagation medium cannot be controlled with ease. Described in Jpn. Pat. Appln. KOKAI Publication No. 6-8138, moreover, is an apparatus in which contact between a grindstone and a rotary dresser is detected by means of a sensor with the aid of a ball that is attached to the dresser. In this conventional apparatus, however, the ball generates noise of a relatively high level as it touches a detection plate. In the case where processing requires use of infinitesimal contact signals, the signal-to-noise ratio is limited and unpractical.
Accordingly, a first object of the present invention is to provide a grinding apparatus capable of grinding grooves on a workpiece with improved efficiency. A second object of the invention is to provide a grinding apparatus capable of enhancing the accuracy of a grindstone to improve the accuracy of work on grooves. A third object of the invention is to provide a dressing method in which the whole surface of a grindstone can be brought securely into contact with a dresser, so that the dressing accuracy is improved to lengthen the life of the grindstone and enhance the dressing efficiency.
In order to achieve the first object described above, a grinding apparatus according to the present invention comprises a rod-shaped grindstone having a distal end portion with a curved surface corresponding to the cross-section of a groove of a workpiece to be ground, a spindle mechanism for rotating the grindstone, supporting means for supporting the grindstone in a manner such that the grindstone is inclined at a given angle to the axis of the workpiece fixed in a predetermined position, and a drive mechanism for bringing the distal end portion of the grindstone into contact with the workpiece and relatively moving the grindstone along the axis of the workpiece without changing the aforesaid angle to the workpiece.
According to this invention, the grindstone has increased stiffness to resist grinding force as it forms a spline ball groove on the inner surface of the workpiece, so that the grinding efficiency and worked groove accuracy are improved. In this invention, the grindstone includes a rod-shaped metallic support member, an inner grindstone layer portion attached to the outer periphery of the support member, and an outer grindstone layer portion fixed to the inner grindstone layer portion so as to cover the outer peripheral surface thereof and having a distal end portion with a curved surface corresponding to the cross section of the spline ball groove of the workpiece. According to this invention, the grindstone and components of its drive system are improved in durability.
In order to achieve the second object, a grinding apparatus according to the invention comprises a rod-shaped grindstone having a distal end portion with a curved surface corresponding to the cross section of a groove of a workpiece to be ground, a spindle mechanism for rotating the grindstone, supporting means for supporting the grindstone in a manner such that the grindstone is inclined at a given angle to the axis of the workpiece fixed in a predetermined position, a dressing apparatus including a rotary dresser having a dress groove with a cross section corresponding to the distal end portion of the grindstone, and a drive mechanism for relatively moving the grindstone along the axis of the workpiece without changing the aforesaid angle, thereby reciprocating the distal end portion of the grindstone between the dress groove and the workpiece.
According to this invention, the rod-shaped grindstone reciprocates between the worked groove of the workpiece and the dress groove, whereby the distal end portion of the grindstone can be shaped every time the groove is worked. In this grinding apparatus, the shape of the groove of the formed dresser is given to the grindstone as the grindstone is dressed, so that the distal end portion of the grindstone can be shaped so as to enjoy an accurate curvature radius. Accordingly, the grindstone can work the groove of the workpiece with high accuracy without rendering the inner surface of the groove undulatory. Thus, the grinding apparatus can accurately work a groove having the shape of a Gothic arch, not to mention a groove with a single curvature radius.
A dressing apparatus according to this invention should comprise a movable supporter, a moving mechanism for moving the supporter, a rotating mechanism mounted on the supporter, a rotary dresser rotatable by means of the rotating mechanism, an AE sensor attached to the rotary dresser and adapted to detect vibration generated when the dresser is brought into contact with the grindstone and to deliver an output based on the vibration, a receiver attached to the supporter in a manner such that the receiver is opposed to the AE sensor across an air gap and capable of receiving the output of the AE sensor, and a controller adapted to deliver a command to stop the movement of the supporter in response to a signal received by the receiver.
According to this invention, the contact between the rod-shaped grindstone and the dresser can be highly accurately detected as the grindstone is dressed.
In order to achieve the third object, a dressing method according to the invention comprises a first positioning process for relatively moving a grindstone in a first direction along the axis of a rotary dresser from a position in which the grindstone faces an inner surface of a dress groove, detecting a first contact position reached the moment the grindstone touches one side edge of the dress groove, and stopping the movement, a second positioning process for relatively moving the grindstone in a second direction along the aforesaid axis, detecting a second contact position reached the moment the grindstone touches the other side edge of the dress groove, and stopping the movement, the second positioning process directly following the first positioning process, a third positioning process for moving the grindstone to an intermediate position between the first and second contact positions, and a dressing process for moving the grindstone toward the inner surface of the dress groove in a direction perpendicular to the axis, thereby bringing a distal end portion of the grindstone into contact with the inner surface of the dress groove, the dressing process directly following the third positioning process.
According to this invention, the whole surface of the grindstone can be brought into contact with the formed dresser in one cycle of the dressing process without being influenced by thermal deformation of a spindle mechanism for the grindstone or a dresser rotating mechanism. According to this dressing method, the dressing accuracy is improved, so that the grindstone can be shaped with a minor bite of dressing. Since the grindstone can be kept from partial dressing, moreover, its life is prolonged, the grinding efficiency is improved, and the groove can be worked with high accuracy.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.